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fix(query-engine): expand self-keyed accumulators in range queries - #587

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fix(query-engine): expand self-keyed accumulators in range queries#587
milindsrivastava1997 merged 2 commits into
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584-range-query-topk-expansion

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Summary

  • execute_range_query_pipeline's single-population branch never called get_keys() on the merged value accumulator, so self-keyed accumulators like CountMinSketchWithHeap (top-k) returned empty over a range instead of expanding into their top-k keys — the instant path already does this via collect_results_same_aggregation.
  • Fix: every group now tries merged.get_keys() first (mirroring the instant path exactly) and only falls back to the precomputed key list when it returns None. This also covers self-keyed accumulators stored under a non-None outer key (real Arroyo/worker.rs ingestion always wraps Some(key), even for empty grouping), not just the None-keyed case from the original report.

Fixes #584.

Test plan

  • cargo test -p query_engine_rust --lib native_range_query_tests — 7 passed, including two new regression tests for Range queries drop self-keyed accumulator expansion (top-k) for single-population metrics #584 (range_query_self_keyed_topk_expands_without_keys_query, range_query_self_keyed_topk_expands_with_non_none_outer_key)
  • Full lib suite: cargo test -p query_engine_rust --lib — 554 passed, 0 failed
  • New tests independently verified red (against pre-fix code) / green (against fixed code)

🤖 Generated with Claude Code

…k) without keys_query

execute_range_query_pipeline's single-population branch used each value
group's own store-level group_key directly and never called get_keys() on
the merged value accumulator, so self-keyed accumulators like
CountMinSketchWithHeap (top-k) returned empty over a range instead of
expanding into their top-k keys — the instant path already does this via
collect_results_same_aggregation.

Now every group tries merged.get_keys() first (mirroring the instant path
exactly) and only falls back to the precomputed key list — the store's
group_key for single-population metrics, or the separate keys aggregation's
expansion for dual-population metrics — when get_keys() returns None. This
also covers self-keyed accumulators stored under a non-None outer key (real
Arroyo/worker.rs ingestion always wraps Some(key), even for empty grouping),
not just the None-keyed case from the original report.

Fixes #584.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
@milindsrivastava1997

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execute_range_query_pipeline's merged.get_keys().unwrap_or_else(|| fallback_keys.clone()) (mod.rs:1612) applies unconditionally to every group, including dual-population groups where keys_query.is_some(). That diverges from the instant path (collect_all_results), which branches globally: when a separate keys aggregation exists, collect_results_separate_keys is used and never consults the value accumulator's own get_keys().

This is reachable in production: count_topk_capability_fallback_pairs_heap_with_key_agg (sql.rs:1443) shows capability-matching pairs CountMinSketchWithHeap (value) with DeltaSetAggregator (keys) — a real dual-population, self-keyed-value config. With this change, each window step now uses the heap's own capacity-limited per-window top-k instead of the keys-aggregation's stable, full key set, so a key with low count in a given window can silently drop out of that step (or the set can flap between steps) even though it's present in the instant-query result and every other window.

The new tests (range_query_self_keyed_topk_expands_without_keys_query, ..._with_non_none_outer_key) only cover the single-population case, so this gap isn't caught by CI.

Suggest gating the merged.get_keys() fallback on whether the group came from the single-population branch, so dual-population groups always use the keys-aggregation-derived fallback_keys — matching collect_results_separate_keys.

…eys_query in range queries

Review on #587 caught a regression: the previous fix called
merged.get_keys() unconditionally on every group's merged value
accumulator, including dual-population groups (separate keys_query
present). collect_all_results (instant path) branches globally on query
shape instead — dual-population always goes through
collect_results_separate_keys, which never consults the value
accumulator's own get_keys() at all. A real, tested capability-matched
config (sql.rs) pairs a self-keyed CountMinSketchWithHeap value
aggregation with a separate DeltaSetAggregator keys aggregation; the
previous fix let the heap's own (window-shifting) top-k keys silently
override the keys aggregation's expansion for that config.

Range queries now mirror collect_all_results exactly: dual-population
groups always use the keys aggregation's expansion, full stop; only
single-population groups let the value accumulator's own get_keys() take
priority (falling back to the store-level group key), which is what #584
actually needed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
@milindsrivastava1997
milindsrivastava1997 marked this pull request as ready for review August 24, 2026 12:23
@milindsrivastava1997
milindsrivastava1997 merged commit 81e58c6 into main Aug 24, 2026
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@milindsrivastava1997
milindsrivastava1997 deleted the 584-range-query-topk-expansion branch August 24, 2026 12:43
milindsrivastava1997 added a commit that referenced this pull request Aug 24, 2026
…-keyed top-k

#587 (fixes #584, top-k self-keyed accumulator expansion for
single-population range queries) landed on main while this branch was
in flight, independently rewriting the same region of
execute_range_query_pipeline that #583's fix rewrote -- both branches
diverged from the same base commit (e8d4d3b).

The two fixes are orthogonal by design, confirmed while reconciling:
dual-population groups (#583's KeysSource::PerStep) never consult the
value accumulator's own get_keys() at all, in either version -- #587's
own PR review explicitly established that invariant (a self-keyed
CountMinSketchWithHeap value paired with a separate DeltaSetAggregator
keys aggregation is a real capability-matched config; the keys
aggregation's expansion must always win for dual-population). So
merging didn't require picking a side, just composing both:

- KeysSource::PerStep (dual-population, #583): resolves expansion
  keys from the keys aggregation, per output step, before ever
  touching the value merge -- unchanged from #583's own commit.
- KeysSource::Fixed (single-population, #584/#587): resolution moves
  to AFTER the value merge -- try the merged value accumulator's own
  get_keys() first (self-keyed, e.g. top-k), falling back to the
  store-level group key otherwise.
- Adopted #587's fix to the None => all_data... branch: changed from
  filter_map (dropping every group_key=None group entirely -- the
  original, pre-#587 bug, which #583 had inherited unmodified since it
  never touched this branch) to a plain map that keeps group_key=None
  groups with an empty fallback list, letting the per-step self-keyed
  check populate the real keys.

git's own 3-way auto-merge produced code that wouldn't compile
(referenced fallback_keys/is_dual_population that don't exist in
#583's KeysSource-based structure) and, separately, silently
mis-aligned two different new tests' closing braces as shared context
in native_range_query_tests.rs -- both caught and fixed by hand rather
than trusted, per the resolving-merge-conflicts skill.

Also extends #587's own
range_query_dual_population_self_keyed_value_still_uses_keys_query
test (previously a single-timestamp check) to add a mid-range keys
change in the same test, so #583's per-step resolution and #587's
self-keyed-override protection are both pinned holding simultaneously,
not just verified as separately-provable-orthogonal.

Verified: 19/19 native_range_query_tests pass (up from 16 pre-merge,
+3 from #587), full workspace suite (cargo test --workspace) 0
failures, cargo clippy --lib --tests clean.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
milindsrivastava1997 added a commit that referenced this pull request Aug 25, 2026
Two fixes from a code review of the #583/#587 merge (PR #595):

- promql.rs: guard keys_tumbling_window_ms against 0. A zero
  window_size_ms on the key aggregation's config would make
  execute_range_query_pipeline's per-step scan_window
  (`while t < window_end { ...; t += step_increment }`) loop forever,
  since t would never advance. The value side is accidentally
  protected from this by validate_range_query_params's
  `step.is_multiple_of(tumbling_window_ms)` check (only 0 is a
  multiple of 0); keys had no equivalent, so added an explicit check.

- mod.rs: distinguish "keys merge succeeded but get_keys() returned
  None" (e.g. a DeltaSetAggregator remove with no matching add
  resolved in this window) from the routine, expected "no buckets in
  this window at all" case. The former now warn!s -- it means a merge
  DID happen but couldn't resolve a key set, which is worth visibility
  on -- while the latter (which fires routinely, e.g. before a key
  first exists, in nearly every dual-population test in this file)
  stays debug! to avoid making normal usage noisy.

Two other findings from the same review were investigated (spawned a
subagent to write confirming/refuting tests, no production changes)
and confirmed real, but are out of scope for this PR -- filed
separately with their proving tests rather than fixed here:

- #600: execute_range_query_pipeline's scan_window steps the bucket
  map by window_size_ms, but Sliding-aggregation buckets are actually
  persisted at slide_interval_ms (confirmed via
  precompute_engine/window_manager.rs). Affects both the keys side
  (introduced by #583) and the value side (pre-existing, predates
  #583/#587 entirely).
- #601: build_bucket_map doesn't sort same-start-timestamp buckets
  before NaiveMerger's sequential fold, which is order-sensitive for
  DeltaSetAggregatorAccumulator with 3+ colliding deltas (2-bucket
  collisions are order-independent via conflict-cancellation, which is
  why this wasn't caught by the earlier 2-bucket collision test in
  this file). Confirmed: same 3 logical deltas, different insertion
  order, different final answer.

Also filed #598 (finish_range_context reads streaming_config twice,
separate momentary read locks -- a hot-reload landing between them
could give the value and key sides inconsistent config generations)
and #599 (DeltaSetAggregator's per-step keys replay is O(range^2) by
design, tracking the already-documented tradeoff outside the design
doc).

Verified: 19/19 native_range_query_tests pass, full workspace suite
(cargo test --workspace) 0 failures, cargo clippy --lib --tests clean.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
milindsrivastava1997 added a commit that referenced this pull request Aug 25, 2026
)

* test(query-engine): add RED tests for per-step keys_query snapshot bug (#583)

execute_range_query_pipeline fetches/merges keys_query once, anchored at
the range's end, and reuses that single snapshot for every output step.
Two new tests reproduce the two failure modes this causes:

- DeltaSetAggregator: a key added partway through the range gets a
  phantom sample at earlier steps, before it actually existed.
- SetAggregator: a key present only in an earlier window is excluded
  from the final (end-anchored) keys fetch entirely, so its whole
  series silently vanishes from the output instead of just its later
  samples.

Both fail against current code (confirmed via targeted
`cargo test --lib native_range_query_tests`); skipping the full-suite
pre-commit hook for this commit since it's expected to fail on these
intentionally-RED tests.

* test(query-engine): check all 4 host-a/host-b x t=1000/2000 conditions

Extend both #583 RED tests to assert presence/absence at every
(key, timestamp) combination instead of just the one that first
demonstrates the bug, via a shared key_has_sample_at helper:

- DeltaSetAggregator (cumulative deltas): host-a present at 1000 and
  2000; host-b absent at 1000, present at 2000.
- SetAggregator (per-window snapshot, no accumulation): host-a
  present at 1000, absent at 2000; host-b absent at 1000, present at
  2000.

Still RED against current code.

* test(query-engine): expand #583 RED coverage to 16 cases + NaiveMerger pin

Extends the RED test suite for the per-step keys_query snapshot bug
(#583) well beyond the original 2 cases:

- SetAggregator/DeltaSetAggregator through the binary-expr arm path
  (build_arm_range_context), not just the plain range dispatch
- A 5-window oscillating add/remove/add/remove/add sequence for
  DeltaSetAggregator, asserted at every intermediate step
- A key change landing on an interior step, not just a range boundary
- Keys and values bucket widths differing (mismatched tumbling
  granularities), which the existing fixtures couldn't expose since
  both aggregations shared one window size
- Multiple independent groups (real grouping_labels): one group's
  key change must not leak into another's per-step output, including
  a sharper simultaneous-cross-add variant
- A group with keys but zero value data anywhere, which today
  hard-fails the entire range query instead of being skipped
- SetAggregator merging multiple colliding same-timestamp buckets
  within one window (previously only ever exercised with exactly one
  bucket per window)

Also adds `assert_all_at`, a shared mismatch-collector so these
multi-assertion tests report every divergence in one panic instead of
stopping at the first failing assert, and
`create_range_engine_dual_input_with_windows`, a superset of the
existing fixture helper that lets value/key aggregations use
different bucket widths.

Separately pins (GREEN, not RED) that NaiveMerger's sequential
pairwise fold -- not a flat merge_accumulators call -- is what makes
DeltaSetAggregator's add/remove/add/remove/add replay chronologically
correct; the fix this test suite is driving toward depends on that
distinction and it's easy to get backwards.

16 tests total: 5 green, 11 RED. Design rationale for each case
recorded in docs/583-range-keys-per-step-design.md.

Skipping the full test/lint pre-commit hooks for this commit since
it's expected to fail on these intentionally-RED tests (same as the
precedent commit 15bb61e on this branch).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* docs(query-engine): record #583 fix design discussion

Recap of the grilling session that produced the RED test suite in
13d945e and the implementation plan it's driving toward: bug
recap, 8 numbered design decisions with reasoning (architecture, the
generic keys_query widening formula, recompute-vs-incremental
tradeoff, NaiveMerger ordering correctness, do_merge, non-fatal
missing-group handling, cross-group isolation), and the full RED
test inventory mapped to which decision each one pins.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix(query-engine): widen keys_query per range step, stage 1 of 583 fix

Stage 1 of the #583 fix (per-step keys_query in range queries):
plumbing only, behavior-inert on its own -- confirmed via
`cargo test --lib native_range_query_tests` showing the exact same
5 passed / 11 failed split before and after this change.

RangeQueryExecutionContext gains keys_lookback_ms and
keys_tumbling_window_ms (both None when there's no separate
keys_query), populated in finish_range_context by widening
keys_query the same way values_query already is: lookback is derived
from the instant window create_keys_query_params already computed
(end - start), then start_ms.saturating_sub(lookback) re-anchors it
across the whole range. This needs no AggregationType branching --
for SetAggregator the instant window is [end-window_size, end], so
this produces a normal sliding window; for DeltaSetAggregator the
instant window is [0, end], so the lookback equals end_ms and
saturating_sub gives 0 for every current_time in the per-step loop
(current_time <= end_ms always holds), i.e. "replay from the
beginning," for free.

Nothing consumes these two new fields yet -- that's stage 2, which
actually replaces execute_range_query_pipeline's single global
keys merge with the per-step one these fields make possible.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* style(query-engine): cargo fmt native_range_query_tests.rs

Pre-existing drift from the RED-test commit (13d945e), which used
--no-verify to skip the (then-failing-for-unrelated-reasons)
pre-commit test hook and never actually ran through cargo fmt. No
semantic change. Using --no-verify here too: the cargo-test hook
stashes unstaged changes before running, so with stage 2's mod.rs
changes still unstaged at this point it would (correctly) see only
stage 1's code and report the still-expected 11 RED tests -- not a
real failure, just a false negative from splitting a pure-formatting
commit ahead of the logic commit that depends on it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix(query-engine): per-step keys merge in execute_range_query_pipeline, stage 2 of 583 fix

Stage 2 of the #583 fix: the actual per-step keys merge. All 16
native_range_query_tests pass (5 that were already green, 11 that
were RED), plus the full workspace suite (cargo test --workspace,
0 failures across every crate).

What follows is exactly what was explained before making this change:

1. Replace the single keys fetch+merge with a raw fetch. Delete the
   fetch_and_merge_keys(...) call; replace with
   execute_store_query(&context.base.store_plan.keys_query) when
   Some -- same call the values side already uses, giving raw
   (unmerged) buckets, same shape as all_data.
2. Change what `groups` carries. Today each group carries a fixed
   Vec<KeyByLabelValues> (the one-time merged snapshot). Replaced
   with a small KeysSource enum: Fixed(Vec<KeyByLabelValues>) for
   single-population groups (unchanged -- they never had a per-step
   keys concern), or PerStep(&Vec<TimestampedBucket>) for
   dual-population groups -- a reference to that group's raw keys
   buckets, not yet merged.
3. Q6, at group-construction time. Where the code today does
   all_data.get(group_key).ok_or_else(|| "No value for key")? (hard-
   fails the whole query), changed to warn! + skip that one group
   via filter_map.
4. Inside the per-group loop, mirror the value side's own pattern
   exactly. The value side already builds a bucket_map once per
   group, then re-derives window_buckets fresh every current_time
   iteration. Added the identical second copy of that pattern for
   keys: build a keys_bucket_map once per group (only for PerStep
   groups), then inside the current_time loop, do the same windowed
   scan-and-merge -- using context.keys_lookback_ms/
   context.keys_tumbling_window_ms from stage 1 instead of the value
   side's fields -- to get expansion_keys fresh at every step,
   instead of reusing one fixed set.
5. One new call flagged rather than snuck in: if a step's
   keys-window merge comes back empty or get_keys() returns None
   (e.g. DeltaSetAggregatorAccumulator with unresolved removals),
   that's treated as "skip this step's sample for this group" -- not
   a hard error. That's a natural extension of Q6's "non-fatal"
   philosophy to a narrower case (a specific step's keys, not a
   whole group's), but it wasn't explicitly one of the 8 grilled
   design decisions, so it was flagged and confirmed before
   implementing rather than decided silently.

Two follow-up questions were asked and answered before implementing:

Why step 1 (raw fetch instead of fetch_and_merge_keys)? --
fetch_and_merge_keys does two things: raw fetch, then
merge_precomputed_outputs collapses all the fetched buckets into one
merged accumulator per group. That collapse is literally Bug 1: once
buckets are merged together, there's no way left to ask what the key
set looked like at t=1000 specifically -- that information is gone.
To merge per-step, the loop needs the raw, unmerged buckets still
available when it reaches current_time, so it can merge only the
subset whose start < current_time at each step. Calling
fetch_and_merge_keys throws that away before the loop even starts.
This mirrors how values already work: execute_store_query (raw
fetch, no merge) happens once up front; merging happens later,
per-step, via bucket_map + NaiveMerger. Keys need that same split --
step 1 is what makes step 2 possible at all, not an independent
cleanup.

Why the KeysSource enum in step 2? -- Two genuinely different cases
exist for a group's expansion keys, carrying different data:
single-population has no separate keys_query, so the value's own key
IS the output key at every timestamp, unconditionally -- nothing to
look up or merge (today's existing None branch, unchanged).
Dual-population's key set has to be recomputed from raw keys
buckets, per-step -- that's the whole fix. `groups` needs one
uniform element type, but "how to get this group's expansion_keys"
is fundamentally different shaped data for the two cases -- an
already-final Vec<KeyByLabelValues> vs. a &Vec<TimestampedBucket>
still needing per-step work. Two separate Option fields (one per
case, "exactly one is ever Some" by convention) would allow invalid
states (both Some, both None) that would just have to be trusted not
to happen. The enum makes "it's one or the other, never both" a
compile-time guarantee instead of a convention -- for mission-
critical logic, the type system should rule out the invalid state
rather than the author having to.

A clarifying question was also asked and answered: does
single-population need any new per-step logic too? No --
single-population doesn't need any new per-step logic. The #583 bug
is specifically about a separate keys aggregation whose key set can
drift independently of the value data over time (a
DeltaSetAggregator/SetAggregator snapshot merged once and reused).
Single-population has no such thing -- there's only one aggregation,
and group_key (the value bucket's own stored key) IS the output key,
permanently, by construction. expansion_keys = vec![group_key.clone()]
isn't a merge result that could go stale -- it's a tautology, so
there's nothing for Bug 1 to reuse-across-steps incorrectly. The one
thing that does need to vary per step -- does this key actually have
a sample at this particular timestamp -- is already handled,
correctly, by the existing value-side per-step windowing
(bucket_map/window_buckets, the `if !window_buckets.is_empty()`
check). That logic predates #583, isn't part of the bug, and doesn't
change in this fix; it's exactly the same mechanism dual-population's
key side needs to newly mirror -- single-population already gets it
for free because key and value are the same data.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* refactor(query-engine): extract widen_query_window, dedup values/keys widening

finish_range_context's keys_query widening block (added for #583)
duplicated the exact formula the existing values_query widening
block used: lookback = end - start of the query's current window,
then start = start_ms.saturating_sub(lookback), end = end_ms.
Written inline at the time to keep that stage's diff small and easy
to verify in isolation; noted as a follow-up rather than done then.

Extracts widen_query_window(query: &mut StoreQueryParams, start_ms,
end_ms) -> u64, used for both values_query and keys_query. Behavior-
preserving: full lib suite (564 tests) and the 16 native_range_query
tests unchanged before and after.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* refactor(query-engine): fix stale doc comment, dedup bucket_map/scan_window

Follow-up cleanup from the #583 duplication survey (items 1 and 3;
items 2 and 4 filed as #596 and #597 -- both need a real design
decision, not a mechanical refactor, so left out of this commit).

1. fetch_and_merge_keys's doc comment still claimed it was shared by
   the instant and range paths. False since #583's fix replaced the
   range path's call site with a raw execute_store_query fetch --
   corrected to say so.

2. execute_range_query_pipeline had the same ~10-line pattern written
   twice, once for values and once for keys (#583 introduced the
   second copy): build a bucket_map from (start,end)->bucket tuples,
   then scan a window range collecting matching buckets. Extracted
   build_bucket_map and scan_window as private helpers, used by both
   the value and key sides.

Behavior-preserving: full lib suite (564 tests) and the 16
native_range_query tests unchanged before and after.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* docs(query-engine): update #583 design doc status now that the fix landed

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix(query-engine): warn on unresolved keys merge, guard zero keys window

Two fixes from a code review of the #583/#587 merge (PR #595):

- promql.rs: guard keys_tumbling_window_ms against 0. A zero
  window_size_ms on the key aggregation's config would make
  execute_range_query_pipeline's per-step scan_window
  (`while t < window_end { ...; t += step_increment }`) loop forever,
  since t would never advance. The value side is accidentally
  protected from this by validate_range_query_params's
  `step.is_multiple_of(tumbling_window_ms)` check (only 0 is a
  multiple of 0); keys had no equivalent, so added an explicit check.

- mod.rs: distinguish "keys merge succeeded but get_keys() returned
  None" (e.g. a DeltaSetAggregator remove with no matching add
  resolved in this window) from the routine, expected "no buckets in
  this window at all" case. The former now warn!s -- it means a merge
  DID happen but couldn't resolve a key set, which is worth visibility
  on -- while the latter (which fires routinely, e.g. before a key
  first exists, in nearly every dual-population test in this file)
  stays debug! to avoid making normal usage noisy.

Two other findings from the same review were investigated (spawned a
subagent to write confirming/refuting tests, no production changes)
and confirmed real, but are out of scope for this PR -- filed
separately with their proving tests rather than fixed here:

- #600: execute_range_query_pipeline's scan_window steps the bucket
  map by window_size_ms, but Sliding-aggregation buckets are actually
  persisted at slide_interval_ms (confirmed via
  precompute_engine/window_manager.rs). Affects both the keys side
  (introduced by #583) and the value side (pre-existing, predates
  #583/#587 entirely).
- #601: build_bucket_map doesn't sort same-start-timestamp buckets
  before NaiveMerger's sequential fold, which is order-sensitive for
  DeltaSetAggregatorAccumulator with 3+ colliding deltas (2-bucket
  collisions are order-independent via conflict-cancellation, which is
  why this wasn't caught by the earlier 2-bucket collision test in
  this file). Confirmed: same 3 logical deltas, different insertion
  order, different final answer.

Also filed #598 (finish_range_context reads streaming_config twice,
separate momentary read locks -- a hot-reload landing between them
could give the value and key sides inconsistent config generations)
and #599 (DeltaSetAggregator's per-step keys replay is O(range^2) by
design, tracking the already-documented tradeoff outside the design
doc).

Verified: 19/19 native_range_query_tests pass, full workspace suite
(cargo test --workspace) 0 failures, cargo clippy --lib --tests clean.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* fix(query-engine): guard scan_window against zero step, embed KeysSource's per-step data

Two fixes from a second PR #595 review pass:

1. scan_window itself now asserts step_increment > 0 instead of
   relying on callers to never pass 0. The earlier fix
   (7312593) only guarded keys_tumbling_window_ms at its one call site
   in finish_range_context; scan_window has two callers (values, keys)
   and shouldn't depend on either having validated its own step
   source -- the value side's protection is itself just incidental
   (validate_range_query_params's step-is-multiple-of check). Kept as
   a release-mode assert!, not debug_assert!: a hung query is a
   production incident.

2. KeysSource::PerStep now carries its bucket_map, lookback_ms, and
   tumbling_window_ms directly as struct fields, built once at
   groups-construction time, instead of three separate Option fields
   at function scope that only stayed in sync by convention -- each
   re-unwrapped via .expect() on every iteration of the per-step loop.
   Same reasoning that motivated choosing this enum over two raw
   Option fields in the first place (see 583-range-keys-per-step
   design doc, "why the KeysSource enum"), just carried all the way
   through instead of partway: make the invalid state (PerStep present
   but a companion value missing) unrepresentable, not merely
   panic-guarded.

Verified: 19/19 native_range_query_tests pass, full workspace suite
(cargo test --workspace) 0 failures, cargo clippy --lib clean.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
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Range queries drop self-keyed accumulator expansion (top-k) for single-population metrics

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